P/S and Gravity Conversion

Allied

I was reading the Heating Q&A which includes the diagram below. I pipe conversions differently (see second diagram). Perhaps I am missing something on the first drawing? Which is correct? Thank You.

Note complete boiler protection (ESBE, 2-way, 3-way, 4-way, or VSI) not shown.

Paul Mitchell_2

Well they both look the same to me

just a differant set up. If anything is differant and it is not explained on the diagram is that you will get a much more even heat out of the system if you convert it to reverse loop. First supply, last return. Sometimes this requires a little extra pipe but it does make a big differance. Most gravity systems are first supply first return.

Mark J Strawcutter

what's missing

on the Q&A diagram is labeling of the left-hand set of mains. The only way that makes any sense is if the top pipe is "old supply" and lower pipe is "old return". My problem with this approach is twofold - let rads on the left set of mains have colder supply water than those on the right, plus the head loss is greater since all water must pass thru 2 rads (may or may not be a problem or good thing)

I prefer method number two. More closely approximates original gravity system with respect to supply temps.

Mark

Allied

Gravity Flow Conversion Piping

This diagram may be better as to what I'm doing.

1. Change piping to reverse return.

2. Constant circulation on primary pump.

3. Non-electric TRVs on radiators that overheat.

Boilerpro_3

I never liked this set up

because the boiler can still run cold for long periods of time. For just a couple dollars more, you can put an Esbe Thermix thermostatic valve in the return to the boiler, eliminate some time playing with the balance valves and get a full temp boiler return as fast as the boiler warms up. Then, once the boiler is warmed up, hot boiler water is allowed to flow to the P/S tees and then out to the system. On Low mass boilers, I have seen the boiler reach 140F operating temp in about 60 Seconds. If you have an atmospheric boiler with stack damper and standing pilot, the start up temp is usually around 120F, so there is almost no time that the boiler is firing at condensing temps.

I have gone back to do clean and checks on boilers set up with P/s with Esbe's and after three seasons have no rust whatsoever in the burner trays, just a little dust and ash. The heat exchanger's are as clean as the day they were put in.

Boilerpro

Mark J Strawcutter

better yet

put TRVs on all rads which will eliminate the need for reverse return. Constant circ on system (primary) loop but with outdoor reset controlling the boiler/secondary loop.

Mark